Methods are provided for treating a gastric cancer patient. A specific Met fragment peptide is precisely quantitated by SRM-mass spectrometry directly in gastric tumor cells collected from gastric tumor tissue that was obtained from the cancer patient and compared to a reference level. If the Met peptide is below the reference level a second therapeutic regimen is used to treat the patient whereas if the Met peptide is above the reference level then a first therapeutic regimen combining, for example, the second regimen with one or more Met inhibitor therapeutic agents may be used to treat the patient.